In the drilling of deep bore holes for the exploration and extraction of crude oil and natural gas, the “rotary” drilling technique has become a commonly accepted practice. This technique involves using a drill string, which consists of numerous sections of hollow pipe connected together and to the bottom end of which a drilling bit is attached. By exerting axial forces onto the drilling bit face and by rotating the drill string from the surface, a reasonably smooth and circular bore hole is created. The rotation and compression of the drilling bit causes the formation being drilled to be successively crushed and pulverized. Drilling fluid, frequently referred to as “mud”, is pumped down the hollow center of the drill string, through nozzles on the drilling bit and then back to the surface around the annulus of the drill string. This fluid circulation is used to transport the cuttings from the bottom of the bore hole to the surface where they are filtered out and the drilling fluid is re-circulated as desired. The flow of the drilling fluid, in addition to removing cuttings, provides other secondary functions such as cooling and lubricating the drilling bit cutting surfaces and exerts a hydrostatic pressure against the bore hole walls to help contain any entrapped gases that are encountered during the drilling process.
To enable the drilling fluid to travel through the hollow center of the drill string, the restrictive nozzles in the drilling bit and to have sufficient momentum to carry cuttings back to the surface, the fluid circulation system includes a pump or multiple pumps capable of sustaining sufficiently high pressures and flow rates, piping, valves and swivel joints to connect the piping to the rotating drill string.
Since the advent of drilling bore holes, the need to measure certain parameters at the bottom of the bore hole and provide this information to the driller has been recognized. These parameters include but are not limited to the temperature and pressure at the bottom of a bore well, the inclination or angle of the bore well, the direction or azimuth of the bore well, and various geophysical parameters that are of interest and value during the drilling process. The challenge of measuring these parameters in the hostile environment at the bottom of the bore well during the drilling process and somehow conveying this information to the surface in a timely fashion has led to the development of many devices and practices.
One method to gather information at the bottom of the bore well, frequently referred to as “surveying”, is to stop the drilling process, disconnect the fluid circulation apparatus at the swivel joint and lower a measuring probe down the center of the hollow drill string to the desired depth using a cable and after making a measurement, by using mechanical timers or an electronic delay, pull the probe back out of the bore hole and retrieve the information at the surface before resuming the drilling process. This method has many clear and apparent disadvantages, such as the need to stop drilling for an extended period of time, the need to stop fluid circulation and bear the risk of having the drill string stuck in the hole or have the bore well collapse around the drill string. In addition, the need to make several successive closely spaced measurements cannot be met without spending an inordinate amount of time surveying and very little time actually spent drilling the bore well.
An improvement on this method is to have the measurement probe installed into the drill string and have it connected to a long continuous length of cable. This cable, which may have one or several conducting wires embedded in it, is run through the hollow center of the drill string to the surface. This cable can be used to provide power to and to transmit data from the probe back to the surface. Although this method allows for the ability to make successive and rapid measurement of the parameters of interest, it too has several disadvantages in that the cable also requires a swivel joint at the surface with the capability to feed electrical signals through it while maintaining a tight seal and contain high pressures all while being rotated. In addition, this method has the added disadvantage in that as extra lengths of drill string are added to drill deeper, the cable and attached probe will have to be removed from the drill string completely, the new length of drill string attached, and the cable and probe re-inserted into the bore well. As drill strings tend to be of roughly constant lengths of approximately 30 feet (10 meters), this method at best allows for surveying to be done uninterrupted for only this length.
There are obvious advantages to being able to send data from the bottom of the well to the surface while drilling without a mechanical connection or specifically using wires. This has resulted in tools often referred to as “measurement while drilling” or “MWD” for short which will be discussed in greater detail below. Types of MWD tools contemplated by the prior art have been such things as electromagnetic waves or EM (low frequency radio waves or signals, currents in the earth or magnetic fields), acoustic (akin to sonar through the mud or pipe and using mechanical vibrations) and pressure or mud pulse (sending pulses through the mud stream using a valve mechanism) which will also be discussed at greater lengths below.
U.S. Pat. No. 2,225,668, issued Dec. 24, 1940 is an example of an apparatus that proposes imparting electrical currents into the formation surrounding the bore well and inducing alternating currents that can be detected at the surface using widely spaced receivers. Even though this patent shows the measuring probe as being suspended in the bore hole using a cable, variants of this concept wherein the measuring probe is built into the drill string and the data is transmitted wirelessly using alternating currents in the earth have since been proposed and successfully used.
U.S. Pat. No. 2,364,957, issued Dec. 12, 1944 describes such a device wherein the measuring device is built into the drill string and the data is transmitted wirelessly to the surface using electrical signals in the formation.
U.S. Pat. No. 2,285,809, issued Jun. 9, 1942 is an example of an apparatus that proposes imparting mechanical vibrations onto the suspending cable used to lower the measuring probe into the well bore. These mechanical vibrations travel up the suspending cable and are detected at the surface and decoded.
As with the previous examples, this invention proposes that the measuring probe be suspended by a cable into the bore well. Variants of this concept have since been proposed wherein the sensing probe is built into the drill string and the vibrations are imparted onto the drill string itself.
U.S. Pat. No. 2,303,360, issued Dec. 1, 1942, describes such a device wherein the measuring device is built into the drill string and the data is transmitted wirelessly to the surface by imparting vibrations onto the drill string and earth, which are detected at the surface.
U.S. Pat. No. 2,388,141, issued Oct. 30, 1945, is another example of a device wherein the measuring device is built into the drill string and the data is transmitted wirelessly to the surface by imparting vibrations onto the drill string and earth, which are detected at the surface.
U.S. Pat. No. 3,252,225, issued May 24, 1966, is yet another example of a device wherein the measuring device is built into the drill string and the data is transmitted wirelessly to the surface by imparting vibrations onto the drill string that are detected at the surface.
Many more example of devices similar to these listed previously can be found in the literature, however further listing of these devices will be stopped as their practical usability in the drilling environment has been severely limited due to certain mitigating factors. In the case of devices that propose the usage of electrical or magnetic signals in the earth, the significant attenuation caused by the earth and certain types of formations limit the depth to which these devices can be successfully deployed. The ability to effectively deliver sufficient electromagnetic energy into the formation is limited by the available power sources and as such, the attenuation of the signals cannot be overcome with any degree of effectiveness.
Devices that impart vibrations onto the drill string and earth are limited by the attenuation of the signal due to the threaded connections between lengths of drill string and due to the inherent attenuation of the signal as it travels long distances along the drill string. In addition, these methods have proven unreliable to be used while drilling as the action of the drilling bit cutting the earth imparts vibrations onto the drill string, which overwhelm the signal being sent. These types of apparatus have been predominantly limited to surveying only when drilling is suspended.
In response to the many limitations of the previously described technologies and proposals, the use of pressure pulses to encode and send data to the surface of the earth has gained popularity and has remained the predominant method by which data is transmitted from the bottom of a well bore to the surface.
U.S. Pat. No. 1,854,208, issued Apr. 19, 1932 is an early example of a proposed apparatus that measures the angle of the well bore being drilled and as this measurement exceeds a predetermined threshold, closes a valve in the drill string so as to create a substantial pressure pulse that is detectable at the surface.
U.S. Pat. No. 1,930,832 issued Oct. 17, 1933 is another example of a proposed apparatus that measures the angle of the well bore being drilled and as this measurement exceeds a predetermined threshold, closes off the flow in the center of the drill string completely so as to create a substantial pressure increase that is detectable at the surface.
The apparatus listed above all rely on a purely mechanical action to create a flow restriction to create a pressure pulse. U.S. Pat. No. 1,963,090 issued Jun. 19, 1934 is an example of a proposed device that uses a battery power source and an electro mechanical sensing element to close a valve when the well bore deviation exceeds a threshold and to reopen it when the well bore threshold falls below the threshold.
U.S. Pat. No. 2,329,732 issued Sep. 21, 1943 is an example of a particularly successful concept wherein a purely mechanical device is used to measure the well bore inclination and transmit it to the surface using pressure pulses. Significantly improved variants of this proposed device are still being used in large numbers at the time of writing of this document. Devices of this nature vary the number of pulses that are sent to the surface depending on the well bore inclination measured. U.S. Pat. Nos. 2,435,934, 2,762,132, 3,176,407, 3,303,573, 3,431,654, 3,440,730, 3,457,654, 3,466,754, 3,466,755, 3,468,035 and 3,571,936 are a representative sample of the improvements and variations to this concept that have been proposed since its genesis. These variations include the ability to measure other parameters than well bore inclination and also include improvements that allow the usage of the time between the pressure pulse signals in addition to the total number of pressure pulse signals to encode information.
The devices listed above do have certain limitations in that they are non-reciprocating in nature. The measurements in these devices are made when the fluid flow is stopped for a short period of time and the data is transmitted only once when the fluid flow resumed. The advantage of having a downhole measurement while drilling device that can measure parameters whenever desired (not just when the fluid flow is interrupted) and transmit these parameters to the surface continuously or when desired, is readily apparent.
U.S. Pat. No. 2,700,131 issued Jan. 18, 1955 is an early example of a fully realized measurement while drilling tool wherein a pulsing mechanism (pulser) is coupled to a power source (in this case a turbine generator capable of extracting energy from the fluid flow) a sensor package capable of measuring information at the bottom of a well bore and a control mechanism that encodes the data and activates the pulser to transmit this data to the surface as pressure pulses. The pressure pulses are recorded at the surface by means of a pressure sensitive transducer and the data is decoded for display and use to the driller. U.S. Pat. Nos. 2,759,143 and 2,925,251 are other examples of such devices and detail fully realized MWD tools.
U.S. Pat. No. 3,065,416 issued Nov. 20, 1962 details a device where the main pulsing mechanism is open and closed indirectly by using a servo mechanism. This is an early representation of a mechanism that allows the fluid flow to do most of the work of opening and closing the valve and thus generating pulses. Other representative examples of servo driven pulser mechanisms have been proposed in U.S. Pat. Nos. 3,958,217, 5,333,686 and 6,016,288.
U.S. Pat. No. 4,351,037 issued Sep. 21, 1982 is an example of a variant to the pressure pulse generation mechanisms listed whereby a pulse is created not by creating a restriction to the flow if drilling fluid in the hollow center of the drill string, but by opening a closing a port on the side of the drill string. This methodology, often referred to as “a negative pulser”, creates pressure decreases (as opposed to pressure increases) as venting fluid through a port in the dill string allows for some portion of the fluid to bypass the nozzles in the drilling bit.
U.S. Pat. No. 4,641,289 issued Feb. 3, 1987 is an example of a hybrid proposed pulsing mechanism whereby a positive pulser (one capable of creating positive pressure pulses) is coupled with a negative pulser (one capable of creating negative pulses) to provide the ability to create pressure pulses of various shapes and sizes by combining the action of both types of pulsers.
U.S. Pat. No. 4,847,815 issued Jul. 11, 1989 is an example of a “siren” type pulsing mechanism. This mechanism creates positive pulses of reasonable magnitude in rapid succession and in a continuous fashion (as opposed to creating single pulses on demand) so as to generate a hydraulic carrier wave. Data is transmitted to the surface by varying the frequency of the pulses being generated or by creating phase shifts in the carrier wave. Other examples of siren type pulsers are proposed in U.S. Pat. Nos. 3,309,656 and 3,792,429. Another known problem with this type of prior art is that configuration of the blades allows constant exposure to fluid flow and results in faster erosion due to the linear arrangement of the valve to fluid flow.
Currently in the industry, simple probe type devices generally fall under two categories. The first general category is slickline tools. When well bore measurements needed to be made, the drill pipe is pulled a few feet off bottom and the Kelly is disconnected. A probe is then connected to the slickline, usually a reel of solid stainless steel wire of approximately 0.1″ diameter, on the rig floor and the probe is inserted through the I.D of the drill pipe until the probe is seated near the bottom of the pipe and typically a few feet above the bit. The probes usually have some form of a timer, traditionally a mechanical clock with a timer. When the timer expires, the measurement is made and the probe is pulled back out of the drill pipe and the recorded information is retrieved from inside the probe which may utilize a pendulum on a pivot and a paper disk. When the timer expires, a spring loaded pin fires and the angle of the well is punched onto the paper. Newer versions of such tools use digital processors, flash memory and batteries to enable multiple timed measurements and the ability to record various measurements. But the basic limitation is the need to lower and retrieve them from the bottom of the well through the drill pipe using the slick line.
The second general category is wireline tools. The next generation above the slickline tools, allow the transmission of data through a wireline. This is usually an insulated conductor line sheathed in steel and mounted onto a big truck. The wireline, which may be one or more conductors up to a reasonable number of 7 or 8 conductors, allows power to be sent down to the probe and the data transmitted up in real time. These tools are primarily used in open hole or cased hole applications where the drill pipe is not in the well bore and they are predominantly used to measure lithological data as needed between bit runs or before the well is completed for production. Some of these tools were then later modified to allow data to be gathered and sent up to the surface while drilling by inserting the tool through the drill pipe like slickline tools.
This involves the use of special slip ring connectors, high pressure packers to seal around the wire and other highly specialized equipment which allows the drill pipe to be rotated while the cable at the surface does not. A real limitation of these tools is that wireline comes in lengths thousands of feet long, typically mounted on a big truck, while drill pipe is generally 30 ft long. So the tool probe has to either be removed from the Drill Pipe ID every joint or the wireline has to be built with disconnect points and splices. This is often very cumbersome and has other drawbacks that have been previously discussed.
Of these options, the first one to successfully achieve the goal of data telemetry to the surface without wires was mud pulse and therefore the MWD has become synonymous with mud pulse in the industry. The prior art did not, however, lead to viable products at industry wants. See U.S. Pat. Nos. 2,978,634 and 3,052,838. Its introduction and the continual development efforts of many competing parties eventually lead to the first electronic MWD tool in the late 70's. See U.S. Pat. Nos. 4,520,468 and 3,958,217. These tools measured parameters downhole using processors and batteries and transmitted them to the surface using a “mud pulser”.
As generally discussed above, the primary and dominant piece of information that is essential in MWD is inclination or simply the angle of the bottom of the well. It is essentially impossible to drill a straight or vertical well bore. Therefore periodic measurements of the angle of the bottom together with even a rough idea of the depth of the bit allows the plotting of a “worst case” deviation of the bottom of the well from the well head. This essentially requires straight forward trigonometry.
The term “worst case” is used because oil wells have a nature to spiral towards their target due to the cumulative effects of counter torque applied by the drill bit onto the formation. To pin point the location of the bottom of the well requires three things. The first, is generally accurate depth usually referred to as MD for measured depth. The length of pipe is always longer that the actual vertical depth of the well because the hole is never straight and often curved and spiraled. Second is inclination and the third is azimuth. This provides the direction that the bottom of the well is pointing towards at periodic intervals which is generally measured at the same time as the inclination and almost always at the same depth.
With these three pieces of information, which are essentially 3D vectors distributed in space, a “curve” can be fit between them to draw a reasonable representation of the shape of the well bore being drilled and therefore “project” the location of the bottom of the hole relative to the well head. This has very clear implications to staying within lease limits, hitting the right target, and the overall success and profitability of the well itself. In addition, states require specific rules to be followed as far as surveying wellbores are concerned. For example, it is believed to be a requirement for a permitted straight hole in Texas to be within 6 degrees of vertical.
There are dozens if not hundreds of other parameters that can be measured, but most of those are pertinent to directionally drilling wells and logging wells. It is often considered that these types of wells represent a higher end market as opposed to straight hole applications. In more typical straight hole operations, it is still desirable to measure angle and azimuth and send the information to the surface. This when combined with the depth information that the rig already has, allows the curve and shape of the wellbore to be determined and more importantly, the location of the bottom of the well to be estimated.
Most MWD tools were developed for the higher end of the market. These have typically been used, primarily, to help in the drilling of directional wells. These markets require that in addition to inclination and azimuth, a third measurement “toolface” be sent to the surface. In general, toolface helps the driller orient the bottom hole assembly and therefore steer the well in the desired direction. In order to properly steer the well, toolface needs to be sent up continuously (three to four time as a minute). Toolface needs to be sent up all the time. The other measurements, angle and azimuth, are usually made every 100 or more feet on demand. Since original MWD tools were built to serve this market, it restricted the development of the tools in the following way; more data at faster intervals means faster pulsers; faster pulsers usually mean more power consumption; this usually means longer tools for bigger batteries; and it also generally means mechanically flexible (flexible tools are typically better to steer with as they bend around curves).
It is understood that the environment of drilling leads to an unfriendly environment for downhole tools. It is not unusual for the bottom hole temperatures to be up to 150-175 C, well depths to be 15,000 feet to 25,000 ft on average, the associated pressure caused by the weight of mud column to be 20000 psi, high degrees of vibration caused by the typical close proximity to the bit cutting rock which may be within feet, and “slim hole” applications wherein drill pipe is relatively small diameter with maybe a couple of inches in diameter total to work with. Further, accuracy issues arise in these conditions such as directional drilling usually requires relatively precise sensor data to accurately steer the well. The sum of the previous typically means expensive operations.
Traditional MWD tools are expensive to build and expensive to operate. And most in the consuming industry who drill straight holes could not afford them in the early days. In addition, these tools were finicky and required constant monitoring and maintenance. All this leads to a situation where MWD are generally hard to build and operate in the first place and they are relegated to the higher end of the industry. This is the direction that most have pushed this technology in the last 30 years.
In the prior art, there are still numerous straight holes being drilled everywhere everyday. The industry still needs to survey and today their options are generally slicklines that are time consuming and risky such as but not limited to the fact pipe tends to get stuck if operators do not circulate the fluid; wireline which are often impractical and almost as expensive as MWD; and full MWD which is expensive.
The field of measurement while drilling (MWD) is reasonably mature and there are numerous apparatus and devices that have been developed and used over the years to provide a variety of different measured parameters to the driller. As previously outlined, these range from the simplest measurement of the temperature at the bottom of the bore hole to fully integrated products that provide a full range of measurements including but not limited to inclination, azimuth, toolface (rotational orientation of the bottom hole assembly), pressures, temperatures, vibration levels, formation geophysical properties such as resistivity, porosity, permeability, density and insitu formation analysis for hydrocarbon content.
However, there are several limitations both in the capability and in the usability of the available products as has been generally discussed above. Due to the harsh nature of the downhole drilling environment, MWD tools necessarily have to be robust in design and execution. In addition, the constant flow of drilling fluid through or past the MWD tool causes significant erosion of exposed components and can cause significant damage to tools if improperly designed or operated.
It is understood that the term “drilling fluid” is used here to represent an extremely wide variety of water or oil based liquids of varying densities, viscosities and contaminant content. The need to keep the bore hole hydrostatic pressures high in order to contain or reduce the risk of a gas pocket from escaping the bore well results in the drilling fluid being weighted with additives to increase its density. These additives often tend to be abrasive in nature and further exasperate the erosion problems associated with the flow of the fluid past the tool.
In addition, the need to preserve and maintain the quality of the bore well and to prevent or reduce the risk of the bore well caving in, other filler materials are added to the drilling fluid to aid in bonding the bore well walls. These filler materials tend to be granular in nature and clog or cover inlet and outlet ports, screens and other associated hydraulic components that are part of most MWD tools.
Further, the extreme temperatures and pressures that are present in the bottom of the bore well often necessitate the use of expensive and exotic sealing mechanisms and materials, which increase the costs of operating the MWD tools, and thereby reduce their usability to the wider market place.
Still furthermore, due to the high costs associated with drilling oil and gas bore holes, any time that is spent repairing, maintaining or servicing failed or non functional equipment results in a severe reduction in the productivity of the whole drilling operation. As such, MWD tools have always needed to be designed, built and operated with a need for high quality and reliability.
All these and other factors not listed combine to make the design, manufacture and use of MWD tool an expensive prospect for the industry and therefore result in high costs for the customer, the driller. These high costs tend to make MWD tools unavailable or unaffordable to the majority of the drilling market. Although MWD tools that are capable of providing sufficient information to the driller in a reasonably effective manner have been limited to the higher end drilling operations, usually those involving drilling in high cost environments (such as offshore drilling platforms) or in specific limited markets (such as directionally drilling well bores), a large portion of the drilling market is predominantly involved in the drilling of straight vertical well bores at relatively low costs and as such, do not have access to a simple, reliable MWD tool that can provide them with the minimum of information that they may require to effectively drill these bore holes.
Thus, there is a need for a product that fills the needs of the industry. It is desirable to fill these needs at rates that are affordable and attractive to the majority of straight hole rigs while providing more information than the prior art. The above discussed limitations in the prior art is not exhaustive. The current invention provides an inexpensive, time saving, more reliable apparatus and method of using the same where the prior art fails.